Delta Electronics VFD-S manual C.1 Capacity Formulas, n T + n s k s − 1 = P C 1 ⎢ ⎢, n T + I M ⎢1+

Chapter 8Appendix C How to Select the Right AC Motor Drive

VFD-S Series

C.1 Capacity Formulas

1. When one AC motor drive operates one motor

The starting capacity should be less than 1.5x rated capacity of AC motor drive The starting capacity is

k ⋅ N	⎛	GD	2		N	⎞
	⎜					⎟
	⎜TL +	375		⋅		⎟	≤ 1.5 ⋅ the _ capacity _ of _ AC _ motor _ drive(kVA)
973 ⋅η ⋅ cos ϕ ⎝					tA ⎠

2.When one AC motor drive operates more than one motor

2.1The starting capacity should be less than the rated capacity of the AC motor drive

„Acceleration time ≦60 seconds

The starting capacity is

k ⋅ N	⎡		ns	⎤
	[nT + ns(ks − 1)] = PC1⎢⎢1	+		(ks − 1)⎥⎥	≤ 1.5 ⋅ the _ capacity _ of _ AC _ motor _ drive(kVA)
η ⋅ cosϕ			nT
	⎣			⎦
	⎢			⎥

„Acceleration time ≧60 seconds

The starting capacity is

k ⋅ N	⎡		ns	⎤
	[nT + ns(ks − 1)] = PC1⎢⎢1	+		(ks − 1)⎥⎥	≤ the _ capacity _ of _ AC _ motor _ drive(kVA)
η ⋅ cosϕ			nT
	⎣			⎦
	⎢			⎥

2.2 The current should be less than the rated current of the AC motor drive(A)

„Acceleration time ≦60 seconds

	+	⎡	+ n			⎜	− ⎟	⎤	≤	⋅
nT					S	⎛	⎞			1.5 the _ rated _ current _ of _ AC _ motor _ drive( A)
		IM ⎢1		nT		⎝ kS 1⎠		⎥
		⎣						⎦

„Acceleration time ≧60 seconds

⎡	nS ⎛	⎞⎤	≤ the _ rated _ current _ of _ AC _ motor _ drive( A)
nT + IM ⎢1+	⎜ kS −1⎟⎥
⎣	nT ⎝	⎠⎦

C-2 Revision August 2008, SE09, SW V2.61